Paper offset plate for photographic transfer and direct image printing



United States Patent Thisinvention relates to planographic printing plates and the method of making the same. More particularly, the invention relates to printing plates formed by coating a suitable base with a coating composition comprising a pigment, a hydrophilic colloid, and a water-soluble cationic thcrmosetting resin, and insolubilizing said composition upon the base.

Ofiset or planographic printing plates are used to repro- :luce images which have been applied to the pla-nographic surface of the plate. The image is oleophilic in nature in that it attracts oily or greasy substances and is essen-J tially water repellent. The unirnaged portion of the planographic surface is hydrophilic to the extent that it :an easily be wet by water but it can also, before wetting, accept and hold an oily or greasy image. Planographic iurfacesmust'have this hydrophilic-oleophilic balance so :hat the oily or greasy image can be applied thereto and :he unimaged area wet by water. The planographic sur- Face thus prepared and imaged is subjected to treatment 1y an etch solution which prepares the plate for printing. lhe etch solution is repelled by the image portion of the :late but is attracted by the unimaged area. The unmaged area, therefore, is covered by a surface film of :tch solution leaving the image portion alone ink re- :eptive.

A planographic printing plate thus prepared can operate on an oflset printing press whereby the plate is alernatively contacted by a roll supplying-water and a roll :upplying ink. After the image has been inked, it is ransferred from the plate to a rubber blanket and from he blanket to the copy paper.

The printing plates produced according to this invenion are prepared by self-insolubilization methods and hese plates possess an excellent hydrophilic-oleophilic valance permitting good image adherence and good image ife while at the same time permitting good water (or tch solution) retention. Planographic surfaces prepared s disclosed herein produce clean copy, good toning, and ossess good image, correction life, and stop-go" roperties. The printing plates of this invention are of articular value not only in that they may be employed 1 a conventional Direct Image reproduction process as escribed above, but these plates can advantageously e employed in the Verifax (Eastman) process. Veriax is a trade name of the Eastman Kodak Company for hotocopying apparatus and photographic processing hemicals for use in offiee photocopying apparatus.

In the Verifax process, a Verifax Matrix Paper with n emulsion is employed. The emulsion of Verifax latrix Paper is composed of a suspension of silver halide, eveloper and dye-forming components. When the matx is exposed in the copier, the light reaches the emulsion rrough the matrix paper stock. The emulsion in contact ith the clear areas .of the document receives the greatit amount of light. After about seconds in the activarr, these fully exposed areas are hardened so much that my adhere to the matrix and do not transfer.

While the fully exposed areas are hardened, the parally exposed areas (the document image) are dyed and zrtially developed, but not hardened. When the matrix then squeegeed and rolled in contact with Verifax opy Paper, or other suitable commercial paper, a layer the unhardened dyed material, which is still in a gelatinous state, is transferred to the copy paper. By rapidly repeating the wetting, squeegeeing and rolling, the lower layers of unhardened matrix material are successively transferred to sheets of copy paper. In this Verifax process, white areas of the copies stay white because little, if any, material is transferred to them. The image is expected to stabilize to a brown color after some time, but will remain as legible as other business papers.

The printing plates of this invention may also advantageously be employed in the Ektalith (Eastman) process. Ektalith is a trade name of Eastman Kodak Company for photocopying process and apparatus.

Broadly, the invention consists of forming an aqueous coating composition comprising a pigment, a hydrophilic colloid and a water-soluble cationic thermosetting resin.

This aqueous coating composition is then applied in a conventional manner to the surface desired, usually a wet strength paper web, and the coating dried, advantageously at a pH of about 7.0, to effect a cross-linking of the hydrophilic colloid and the water-soluble cationic thermosetting resin to form an insoluble hydrophilic planographic surface.

The type of water-soluble cationic thermosetting resins which may be employed in the practice of this invention are wet strength resins manufactured by Hercules Powder Company under the trade (name Kyrnene 557. These water-soluble cationic thermosetting resins and the methods of making them are described in detail in United States Patent No. 2,926,154.

These resins are prepared by reacting a saturated aliphatic dicarboxylic acid with a polyalkylene polyamine to form a long chain water-soluble polyamide, and then reacting the polyamide with epichlorohydrin to form a Water-soluble cationic thermosetting resin. A resin which may advantageously be employed is prepared byreacting a saturated aliphatic dicarboxylic acid containing 3 to 8 carbon atoms with from about 0.8 to about 1.4 moles, per mole of dicarboxylic acid, of a polyalkylene poly amine to form a long chain water-soluble polyamide, and then reacting the polyamide with epichlorohydrin in a mole ratio of epichlorohydrin to secondary amine groups of the polyamide of from about 0.5 to 1 to about 1.8 to l to form a water-soluble cationic thermosetting resin.

Two hundred twenty-five grams (2.18 moles) of diethylenetriamine and grams of water were placed in a S-necked flask equipped with a mechanical stirrer, thermometer and condenser. To this was added 290 grams (2.0 moles) of adipic acid. After the acid had dissolved in the amine, the solution was heated to 185-200 C. and held there for 1 hours. Then vacuum from a water pump was applied to the flask during the period required for the contents of the flask to cool to C. following which 430 grams of H 0 was added. The polyamide solution contained 52.3% solids and had an acid number of 2.1.

To 60 grams of this polyamide solution in a roundbottom flask was added 225 grams of H 0. This solution was heated to 50 C. and 12.5 grams of epichlorohydrin was added dropwise over a period of 11 minutes. The contents of the flask was then heated to 60-70 C. until it had attained a Gardner viscosity of 15. Then grams of H 0 was added to the product, and it was cooled to 25 C. Eleven ml. of 10% HCl was then added to adjust the pH to 5.0. The product contained 9.0% solids and had a Gardner viscosity of C-D.

Various pigments can be used to form the coating compositions of the printing plates of this invention such as silica, calcium silicate, barium sulfate, titanium dioxide, and clays such as kaolin, e.g. Lustra Clay. Lustra Clay is marketed by the Southern Clay Company. The pigments may be used as a mixture if desired. An example of a combined pigment which has been found to be advantageous is a mixture of about 40% by weight of colloidal silica to about 60% by weight of Lustra Clay.

planographic properties of the plates.

The colloidal silica which can be used according to this invention should contain silica particles of very small size. The main average size of the silica particles should be within a range of from about 7 millimicrons to about 30 millimicrons. Although colloidal silicas containing silica particles of less than 7 millimicrons have not been commercially available, it is believed that the coating compositions of this invention may be advantageously prepared from colloidal silicas containing silica particles of a size even less than 7 millimicrons.

The most advantageous colloidal silicas are those which contain silica particles ranging in size from about 7 to 17 millimicrons. Such colloidal silicas are marketed by E. I. du Pont de Nemoursand Company under thetradenames Ludox S.M., Ludox L.S., and Ludox HS. and

also by the Monsanto Chemical Company under the trade name Syton 200. The types of colloidal silicas and methods of making them are described in detail in United- States Patents No. 2,244,325 issued June 3, 1941, 2,574,- 902 issued November 13, l951,and 2,597,872-issued May 27, 1952.v Such colloidal silicas are generally marketed as a 30% SiO solution. but as described in the above patents the colloidal silica can be prepared containing a higher or lower percent silica.

For many purposes Ludox S.M. is desirable as this material "has a particle size of about 7 millimicrons and enables curing of the coating composition to becarried out in a shorter time. Higher machine speeds can also be used in the production of planographic plates using the Ludox S.M.

Some examples of hydrophilic colloids which can be used and reacted or cross-linked with the water-soluble cationic thermosetting resins according to this invention include amioca starch, chlorinated potato starch, polyvinyl alcohol, sodium carboxymethyl, hydroxyethyl cellulose, chlorinated corn starch, dextrin, sodium carboxymethyl cellulose, methylol polyacrylamide and polyacrylamide. The chlorinated corn starch referred to is an oxidized starch product from common corn starch by treating it in an aqueous suspension with a hypochlorite solution containing a slight excess of sodium hydroxide.

Polyvinyl alcohol has been found to be particularly advantageous.

The amounts of pigment which can be used can vary quite widely depending upon the particular hydrophilic colloid employed. We have found that a pigment-hydrophilic colloid-ratio of about 2:1 to about 7:1 is generally suitable although both higher and lower ratios can be used. When using sodium carboxymethyl cellulose as the hydrophilic colloid, we have found it to be advantageous to maintain the pigment-colloid ratio about 5:1. Depending upon the hydrophilic colloid employed, the ratio of the Kymene 557 to the colloid may advantageously be from about 30% to about The reaction or cross linking of the hydrophilic colloid with the water-soluble cationic thermosetting resin is advantageously carried out at a pH of approximately 7.0. Salts which may be advantageously used to enhance the planographic properties of the plate include zinc acetate, zinc chloride, zinc phenol sulfonate, zinc sulfamate, zinc silicofluoride, and alum, as well as salts of other divalent and tri-valent metals, e.g. lead, calcium, manganese, cerium, lanthanum. Other suitable salts can, of course, be used. The amount of salt which can be used can be varied widely depending on the particular salt employed. The amount which is utilized can be 4 readily determined by those skilled in the art.

Verifax process it is particularly advantageous to em ploy a coating composition having a pH between about 6 to 9. We have found that the pH of the coating compositions may be adjusted to the proper pH range by the use of acetic acid, ammonia, morpholine, causticsoda and the like.

The coating compositions produced according to this invention are advantageously prepared by first preparing the pigment or pigment mixture, and adding thereto the hydrophilic colloid, while stirring. Next, the watersoluble cationic thermosetting resin is added andthen the salt. The mixing may be done at room temperature and the viscosity of the mixture is advantageously adjusted to about 200 centipoises, Brookfield. The pH can be adjusted by adding ammonia or acetic acid to bring the pH to between 6 and 9 and preferably to about 7.0.

The aqueous coating compositions may be applied to a base web or sheet by conventional apparatus, suchas air knives or roll coaters. The amount of coating may vary from about 2 to 10 pounds per ream of 3300 square feet, with 6 to 8 pounds being most satisfactory. After coating, the stock is dried at normal festoon dryer temv 7' peratures (e.g. 110 F.l F.) to remove moisture. The stock is then cured by exposure to temperatures of about 325 F.350 F. for a period of 2 to 15 seconds. The curing temperature and the curing time of course will depend for example upon the type and amount of salt used, the pH of the coating composition, the particular hydrophilic colloid used, etc. -The optimum time and planographic printing plates were prepared by coating asuitable wet strength paperstock with the aqueous coating composition described therein, and drying and then curing the applied coatings by exposure to a temperature of about 325 F.-350 F. fora period of about 2-15 seconds.

Parts are by weight. 5

' Example I Eighty-four parts of a 6% sodium carboxymethyl cellulose solution were mixed with 26 parts of Lustra Clay (60% suspension) and 32 parts of Syton 200 (30% suspension), 15 parts of Kymene 557 (10% solution), 8 parts zinc acetate (25% solution), and 60 parts water. The pH of the color was adjusted to 6.5 with ammonia. The composition was coated on a paper base and then dried and cured.

Example 2 The procedure followed in Example 1 was followed except that 34 parts of a 15% solution of Penford Gum' No. 280 were used in place of the 84 parts sodium car-. boxymethyl cellulose and 30 parts of water were employed instead of 60 parts of water. Penford Gum 280 is a hydroxymethyl starch ether of a low degree of substitution -manufactured by Penick and Ford Ltd.

Example 3 Two hundred parts of an 8% solution of a high viscosity, 98% hydrolyzed polyvinyl alcohol, marketed by du Pont under the trade name Elvanol 72-51, were mixed with 83.5 parts of Lustra Clay (60% suspension) and 100 parts of Ludox S.M. (30% suspension), 48 parts higher or lower pH may be i f Kymene 557 solution), 4 parts zinc acetate (in 2 parts water) and 10 parts butyl alcohol. The pH of le color was adjusted to 9 with soda ash. The composion was coated on a paper base and then dried and cured.

Example 4 7 Example 5 Eighty nine parts of a 9% solution of a high viscosity, 3% hydrolyzed polyvinyl alcohol, marketed by du Pont ider the trade name Elvanol 72-51, were mixed with l parts of Lustra Clay (60% suspension) and 50 parts Ludox SM. (30% suspension), 5 parts of a hydrated agnesium aluminum silicate (manufactured by Attapul- 1s Minerals & Chemicals Corp. under the trade name ttasorb RVM), 24 parts of Kymene 557 (10% solution), parts zinc acetate (25% solution) and 5 parts of butyl cohol. The pH of the color was adjusted to 9 with da ash. The composition was coated on a paper base 1d then dried and cured. The cured coatings of all the printing plates produced shown in Examples 1 through 5 were hard and watersoluble, and they possessed excellent hydrophilic-01cciilic balances. These printing plates were successfully ed in the Direct Image process, the Verifax and the ttalith processes. Employing small amounts of Attarb were found to improve the tooth and image transfer the resulting plates, particularly when the plates were ed in the Verifax and the Ektalith processes. The printing plates of this invention may advantageousbe used in Xerography. Xerography is a non-chemical totographic process in which the plate is sensitized eleccally and developed by dusting with electrically charged re powder. The Xerography process is more generally scribed, for example, in United States Patent No. 2,919,- 1 issued December 29, 1959. We claim: 1. A planographic printing plate comprising a base and, hered thereto, an insolubilized coating which comprises pigment and the reaction product of a hydrophilic cold and a water-soluble cationic thermosetting resin prered by reacting a saturated aliphatic dicarboxylic acid ntaining 3 to 8 carbon atoms with from about 0.8 to out 1.4 moles, per mole of dicarboxylic acid, of a poly- :ylene polyamine having two primary amine groups dat least one secondary amine group to form a long ain water-soluble polyamide, and then reacting the polylide with epichlorohydrin in a mole ratio of epichlorodrin to secondary amine groups of the polyamide of rm about 0.5 to l to about 1.8 to l.

2. The planographic printing plate of claim 1, in which base is a paper base.

the hydrophilic colloid is polyvinyl alcohol and in which the pigment contains colloidad silica having a particle size between about 7 and millimicrons.

6. The planographic printing plate of claim 5 upon which there is placed an ink-receptive image.

7. The planographic printing plate of claim 2, in which the insolubilizecl coating contains a polyvalent metal inorganic salt.

8. The planographic printing plate of claim 1, upon which there is placed an ink-receptive image.

9. The planographic printing plate of claim 4, upon which there is placed an ink-receptive image.

10. The planographic printing plate of claim 7, upon 0 which there is placed an ink-receptive image.

11. A method of reproducing an image which comprises placing an ink-receptive image upon a planographic surface of a planographic printing plate having a paper base and a planographic coating adhered thereto comprising a pigment and the reaction product of a hydrophilic colloidand a water-soluble cationic thermosetting resin prepared by reacting a saturated aliphatic dicarboxylic acid containing 3 to 8 carbon atoms with from about 0.8 to about 1.4 moles, per mole of dicarboxylic-acid, of a polyalkylene polyamine having two primary amine groups and at least one secondary amine group to form a long chain water-soluble polyamide, and then reacting the polyamide with epichlorohydrin in a mole ratio of epichlorohydrin to secondary amine groups of the polyamide of from about 0.5 to 1 to about 1.8 to 1, contacting the planographic surface with the ink-receptive image thereon with a roll supplying an aqueous fountain solution, then contacting the planographic surface with the ink-receptive image thereon with a roll supplying greasy ink, transferring the greasy ink to a rubber blanket and transferring the ink to a copy paper.

12. The method of reproducing an image according to claim 11 in which the pigment contains a colloidal silica having a particle size between about 7 to about 30 millimicrons.

13. The method of reproducing an image according to claim 11 in which the hydrophilic colloid is polyvinyl alcohol. 4'

References Cited by the Examiner UNITED STATES PATENTS DAVID KLEIN, Primary Examiner.

ROBERT A. LEIGHEY, ROBERT E. PULFREY,

Examiners. 

1. A PLANOGRAPHIC PRINTING PLATE COMPRISING A BASE AND, ADHERED THERETO, AN INSOLUBILIZED COATING WHICH COMPRISES A PIGMENT AND THE REACTION PRODUCT OF A HYDROPHILIC COLLOID AND A WATER-SOLUBLE CATIONIC THERMOSETTING RESIN PREPARED BY REACTING A SATURATE ALIPHATIC DICARBOXYLIC ACID CONTAINING 3 TO 8 CARBON ATOMS WITH FROM ABOUT 0.8 TO ABOUT 1.4 MOLES, PER MOLE OF DICAROBOXYLIC ACID, OF A POLYALKYLENE POLYAMINE HAVING TWO PRIMARY AMINE GROUPS AND AT LEAST ONE SECONDARY AMINE GROUP TO FORM A LONG CHAIN WATER-SOLUBLE POLYAMIDE, AND THEN REACTING THE POLYAMIDE WITH EPICHLOROHYDRIN IN A MOLE RATIO OF EPICHLOROHYDRIN TO SECONDARY AMINE GROUPS OF THE POLYAMIDE OF FROM ABOUT 0.5 TO 1 TO ABOUT 1.8 TO
 1. 8. THE PLANOGRAPHIC PRINTING PLATE OF CLAIM 1, UPON WHICH THERE IS PLACED AN INK-RECEPTIVE IMAGE. 